In a tester used in a post process of semiconductor manufacturing process or an actual mounting device, a vacuum suction device is frequently used for transporting an electronic chip part. In this day, advances in miniaturization and weight reduction increase cases in which an electronic chip part of 20 g or less is handled, and in some cases, extremely light-weighted electronic chip part of about 0.1 g is frequently used. Therefore, the desire to shorten the response time and to enhance the precision of a suction device is increasing.
FIG. 2 shows a vacuum suction device 1 for sucking and transporting such an electronic chip part. The suction device 1 comprises a suction head 2 for sucking an electronic chip part W using negative pressure, a negative pressure source 3 comprising a vacuum pump or the like, a positive pressure source 6 having a positive pressure generating mechanism 6a such as a booster pump and a pressure reducing valve 6b, and a double solenoid-type electromagnetic valve 7 of three position closed center type which selectively brings the negative pressure source 3 and the positive pressure source 6 into communication with the suction head 2. A passage 8 between the positive pressure source 6 and the electromagnetic valve 7 includes a throttle device 9 such as a throttle valve. A passage 10 between the electromagnetic valve 7 and the suction head 2 includes a suction filter 10a for removing dust in the air.
When the suction device 1 transports the electronic chip part W, the electromagnetic valve 7 is first switched over to bring the negative pressure source 3 and the suction head 2 into communication with each other, and the suction head 2 is allowed to suck the electronic chip part W. Then, the electronic chip part W is transported to a destination. After that, in order to separate the electronic chip part W from the suction head 2, the electromagnetic valve 7 is switched over to bring the positive pressure source 6 and the suction head 2 into communication with each other. However, if a positive pressure is supplied into the suction head 2 from the positive pressure source 6, even if the pressure is low, since the electronic chip part W which is reduced in size and weight is blown off from the suction head 2 or a position of the electronic chip part W is deviated, the electronic chip part W can not be supplied to a correct position.
In order prevent such a situation, it seems to be a good idea to sufficiently reduce a flow rate of positive pressure air using the throttle device 9 or to introduce atmospheric air instead of the positive pressure source 6. However, since it takes time until pressure acting on the suction head 2 rises, delay is generated in response time from the instant when the electromagnetic valve 7 is switched to the instant when the electronic chip part W is separated from the suction head 2.
Thereupon, in the vacuum suction device 1 shown in FIG. 2, the electromagnetic valve 7 is switched to a central position immediately before the pressure acting on the suction head 2 reaches a pressure near the atmospheric pressure, and a positive pressure and a negative pressure supplied to the suction head 2 are completely interrupted.
In the conventional vacuum suction device 1, however, the electromagnetic valve 7 of three position closed center type is required, and two solenoids are required to switch the valve and thus, the costs are increased. Further, it is extremely difficult to adjust the switching timing of the electromagnetic valve 7 to the central position and the throttle device 9 and the like while keeping balance therebetween such that the electronic chip part W is precisely separated without generating a delay in the response time.